The present invention relates to an improved annulus pressure responsive sampling apparatus for use in the sampling of well formation fluids in the testing of oil wells.
Various tester valves, circulation valves and sampler valves for testing oil wells have been developed which are responsive to changes in the annulus pressure of the fluid between the well bore and the testing string for the opening and closing of the various valves. These various annulus pressure responsive valves are useful, particularly in offshore testing operations, where it is desired to manipulate the various valves in the testing string without utilizing reciprocation of the testing string thereby allowing the blow-out preventers to remain closed about the testing string.
Typical prior art annulus pressure responsive valves which may be used as sampler valves for obtaining a sample of the formation fluids during the formation testing procedure are described in U.S. Pat. Nos. RE 29,562; RE 29,638; 3,858,649; 4,047,564; 4,063,593; 4,064,937; 4,270,610; 4,311,197; 4,502,537; 4,553,598; and in United Kingdom Patent Application GB No. 2132250A.
In wells where high formation pressures and flow rates are encountered along with sour gas, hydrogen sulfide (H.sub.2 S), being present it is desirable to have an annulus pressure responsive sampler valve which is designed to catch and retrieve samples of formation fluids under such conditions. It is further desirable to have an annulus pressure responsive sampler valve which has an unrestricted bore therethrough after catching a sample of formation fluids so that formation fluids recovered during testing operations may be injected back into the formation or other operations may occur as desired. This is particularly desirable in environmentally sensitive areas where the surface disposal of formation fluids is a problem or prohibited. Moreover, the desirability of maintaining an open, unrestricted bore through a sampler valve is not limited to the above situations, but is generally desirable so that, even if the sampling mechanism is accidentally, inadvertently or even intentionally actuated before or during a test, the test may still continue. The aforesaid U.S. Pat. No. 4,502,537 discloses a valve which attempts to provide this capability. However, that sampler valve does not have a truly unrestricted bore, as the diameter thereof is less than that of normally used tester valves, sampler valves, and other tools employed in a testing string. As a consequence, perforating guns cannot be run through that sampler valve on a wireline, nor can actuating means for tubing conveyed perforating guns be dropped therethrough. In addition, that sampler valve requires the fluid to be sampled to travel through restrictive apertures at the top and bottom of an annular sample chamber in the wall of the tool. Moreover, the actuation of this prior art sampler valve is substantially instantaneous in response to the appropriate level of annulus pressure, thus prohibiting sampling after a time delay, such as after a tester valve thereabove has been closed. Finally, this prior art valve is unduly complex in structure, particularly in the means employed to drain the sample chamber after a test.